The Sub-Mariner is called in to investigate a strange munitions explosion on a British island located in the West Indies. He meets with the governor and Dr. Heinman, a local expert on the occult who him that the locals have have spotted strange "phantoms", something which both men dismiss as superstition, however one of the natives insists that he saw walking dead men involved in the explosion.

At midnight that night at a local military base, and army of zombies rises out of the water and attacks the soldiers. They are led by a cloaked man calling himself the Zombie Master who tosses grenades at the base. When Namor arrives on the scene he witnesses the zombies jumping back into the waters. Diving in after them, he is attacked by one of the zombies. One of Namor's punches knocks off a strange silver headband on the zombies head rendering it inert once more. Namor then pulls it to shore where one of the native boys recognizes it as his brother who died three years previously and buried in Haiti. Namor aids the boy in putting his brother back to his eternal rest.

However, come the dawn the Zombie Master and his minions place another headband on the corpse and tell the boy to get the Sub-Mariner to watch the coffin after the funeral. To Namor's surprise, the Zombie Master appears and orders the dead body of the man -- named Tom -- to rise from his coffin and to swim to the nearby harbor. Namor follows after the zombie, while the Zombie Master returns to his ship which is full of his zombie hordes and his Nazi employer. With their acts of sabotage a complete success, the Zombie Master and his Nazi ally plot their next operation: To send the zombies to assassinate President Roosevelt who is visiting with the governor. They plot to send an army of zombies with explosives to blow up the ship containing the President. Arming some ofthe zombies with knives to deal with the Sub-Mariner should he interfere, the Zombie Master sends his minions on a mission to destroy the undersea monarch.

While Namor is busy fighting off his attackers, the Zombie Master sends the zombie of Tom to destroy the Presidents ship. Having fought off his attackers, Namor swims after Tom and manages to talk sense into him, telling him he is being manipulated by Nazis and about how his brother cried at his death. Tom breaks free from the control of the headband and then swims back toward the Zombie Master's ship when the Zombie Master attacks. Namor subdues him and removes his diving helmet revealing him to be none other than Mr. Heinman. Soon after the ship is destroyed in a massive explosion that destroys the ship. Later, the Sub-Mariner explains the entire incident to the governor.

Baron Schlus, a Nazi spy, arrives at the local aquarium to meet with his fellow operatives. Telling the guard the password he is admitted to a secret section of the aquarium that is the never center of the Nazi spy cell in the area. Nearby, the Sub-Mariner is waiting on Betty Dean to show up for their scheduled date. When Betty is running late, Namor decides to take a look and visit the local aquarium. Inside, he decides to take a dip in one of the fish tanks and ends up nodding off to sleep while relaxing in the water.

While upstairs, the Nazis who are using the aquarium for their headquarters explains to Schlus that their operation gives them view of the waterfront and allows Nazi U-Boats to deliver dynamite supplies to them that they intend to use to sabotage the city. With the operation explains Schlus orders his men to call the boats in at once.

Meanwhile, the Sub-Mariner awakens and realizes he has slept way past his meeting with Betty and is about to leave the aquarium when he stumbles upon the spies discussing their plans. As Namor is busy fighting them Baron Schlus sneaks up behind him and strikes the hero upside the head with a fire extinguisher knocking Namor out.

In order to dispose of the hero, they toss him in an squid tank and leave the creature to destroy him. However, the water revives Namor and he easily slays the squid and escapes from the death trap. Namor goes after the Nazis and finds them in their radio room calling in the U-Boat to bring in the explosives. When Namor attempts to tackle them again, they activate a trap door that lands Namor in a pool of water filled with sharks.

When Namor fights free of the sharks he finds that the spies have already left in a motorboat to meet with the sub. Namor races after them and then forces their motorboat to crash into a buoy, resulting in an explosion that kills the spies. Namor then swims out to the Nazi sub where he subdues the crew and sets it to explode, killing all aboard. The next day, when Namor meets up with Betty he is about to apologize for standing her up when she confesses to answering an emergency and not showing up. Namor accepts her apology tells her that he is an understanding fellow.

Namor has returned to New York City, surfacing in New York Harbor just as an American supply ship is about to leave for the Atlantic is rocked by a massive explosion that sinks the vessel. Searching around for Nazi subs, Namor finds no trace of them and finds that the only other vessels in the water are a number of tug boats. Namor finds this suspicious.

The following day he accompanies another boat leaving port when torpedoes are spotted heading straight for it. Namor dives into the water and redirects it away where it explodes harmlessly at sea. Diving under the water, Namor searches for the source of the torpedos and sees that they are being fire out of the tug boat he saw the day before. Grabbing the next torpedo fired from the ship, Namor redirects it back at the tug, destroying it in a massive explosion.

Realizing the tug boats in the harbor are controlled by Nazi spies, Namor climbs aboard the next one to deal with the crew personally. While fighting with the crew he is struck from behind and knocked out. When Namor comes around, he finds himself inside the tugboat which is really a Nazi U-Boat in disguise. With Namor bound up, the captain of the ship gloats over his plan to destroy American ships in the harbor in subs disguised as harmless tugboats when he is alerted that the supply ship is about to leave the harbor.

The captain of the ship has Namor tired to the torpedo he intends to fire at the American vessel. However as Namor is launched toward the torpedoes target, he manages to break free of his bonds and redirect the torpedo at the Nazi sub, sinking it. Returning to the surface he spots the last of the Nazis aboard a barge which is hiding a massive cannon on board. He tips the ship over, dumping the Nazi agents into the water to drown. Spotting another tug heading toward the Statue of Liberty. Using the remaining torpedoes aboard the barge, Namor destroys the last of the decoy vessels, saving the Statue of Liberty from destruction.

One night, Professor John Barnes comes out of his near exile with a new invention which he plans to turn over to the United States military. However, as he walks in the night he is murdered by a Nazi spy named Karl Kraft, who also steals the scientist's identity and invention.

Returning to the hideout he shares with his fellow spies, he creates a decoy of the invention loaded with explosives and brings it to a meeting at the United States Ordinance Corporation in Washington D.C. Upon delivery the device explodes killing the military officials who had gathered there.

While in New York City, the Angel is having dinner with love columnist Nan Carter. Nan is complaining about having higher aspirations but laments that her editor does not take her ambitions seriously. When the Angel gets the newspaper and reads about how Barnes has been accused of the murder of military officials he believes that it is a frame up job and prepares to head for Washington. Nan convinces the Angel to allow her to come along and cover the story in order to show her employers that she is more than just a love advice columnist. The Angel allows her to come, but warns her not to get in his way.

Arriving in Washington, they begin searching Barnes' home and find nothing out of the ordinary and are about to believe that Barnes sold out to the Nazis when Nan finds a bloody shirt. Searching the property they find Barnes' body outside prompting the Angel to alert the FBI.

His only clue being a laundry mark, the Angel tracks learns that the shirt that Barnes wore was dry cleaned by Karl Kraft but is told Kraft moved away when he goes knocking at the door. Not believing the man, the Angel breaks in through the cellar window but accidentally knocks over some supplies bringing one of the spies downstairs to investigate the noise. The Angel attacks, but is knocked out by the Nazi spies who decide to leave their hideout and relocate someplace else. When the Angel comes around, he gets Nan to assist him in trapping the killer of John Barnes.

Nan knocks at the door and lets slip she knows a secret about the invention prompting the Nazis to take her to see Karl Kraft, unaware that the Angel is following them or that Nan is secretly searching the property for the invention. However, Kraft is not so easily fooled and realizes Nan's true intentions and decides to deal with her himself. Entering the room he threatens to use her to lure the Angel into a trap and kill them both with a time bomb when the Angel suddenly smashes in through the window. The Angel easily trounces Kraft and his men, and then orders Nan to call the FBI. With the crooks rounded up, Nan takes her story to her newspaper and it gets published on the front page.